This invention relates to fusion welding, more particularly to composite filler rods or filler wires of the kind comprising a metallic sheath enclosing a compacted particulate composition which may contain substances from one or more of the following groups: Alloying agents, desoxidizing agents, fluxing agents, slag-forming agents, gas-forming agents and arc stabilizing or electron emitting agents.
Tubular welding wires or rods of the kind referred to are used in gas welding and in arc welding with a non-consumable electrode (carbon arc welding and TIG welding) as well as in the electro-slag welding process (ES welding) and the consumable electrode arc welding process, in which last-mentioned processes the tubular wire or rod does itself constitute the consumable electrode. In automatic or semi-automatic consumable electrode welding the wire is usually supplied as a coil, while in manual welding usually rod-shaped electrodes are employed. The wire or rod is usually bare, but may also be coated.
The existing welding wires or welding rods of the kind above referred to are manufactured by two different methods. In one method, a metal strip is successively shaped into a trough into which the particulate composition is discharged, whereupon the strip is submitted to one or more rolling and/or drawing operations to shape the strip into a tubular sheath firmly enclosing the particulate composition. FIGS. 1b, 1c and 1d of the drawing show examples of the shape of the cross-section of prior-art filler wires manufactured in this way. Even if care is taken to close the joint S between the edges of the strip as well as possible, the joint is never completely air-tight. The sheath therefore does not provide a complete protection for the enclosed material against humidity and contact with the surrounding air. This disadvantage is particularly serious for electrode wires containing a flux composition of the lime basic kind for which the presence even of traces of humidity is harmful.
In the other method, the particulate composition is inserted into a seamless tube the diameter of which is subsequently reduced to the required degree by a drawing process. FIG. 1a represents an example of the shape of the cross-section of a prior-art filler wire made in this way. To make the particulate composition entered through an open end of the seamless tube fill the whole length of the tube, vibration of the tube is employed. To prevent the vibrations from causing segregation of different constituents of the filler composition, the filler has to be of the agglomerated type in which all of the particles have substantially the same composition. This is an undesirable limitation. Also, the filling process is time-consuming and does not always result in a uniform filling along the length of the tube.
The invention has for its principal object to provide an improved filler rod or filler wire of the general type above specified, and an improved method for the manufacture of a filler rod or filler wire of said type which does not suffer from the disadvantages above described.